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In order to fulfill the requirements of a real-time system, a system must react to an external event like an interrupt within a defined time frame. Therefore several mechanisms, configurations and implementation rules have to be considered.

Technical Basics

Currently running tasks with low priority must be preempted to allow the real-time critical task to run. Preemption depends on the rules of the task’s scheduling policy. Another important aspect in a real-time system is the guaranteeing the exclusive use of certain resources for real-time tasks.

Technical details of PREEMPT_RT patch

The main aim of the PREEMPT_RT patch is to minimize the amount of kernel code that is non-preemptible 1). Therefore several substitution mechanisms and new mechanisms are implemented.


There are three categories of HOWTOs:


Several real-time related publications can help broaden your knowledge about real-time systems.

Known Limitations

Some functionality is not available on RT because its implementation is not compatible with RT. Those limitations may apply to the to the kernel as a whole or may apply to specific architecture or platforms.

Go back to Real-Time Main Page

Paul McKenney. A realtime preemption overview.
realtime/documentation/start.txt · Last modified: 2018/08/21 14:31 by ebugden